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Re^2: creating qr from existing regex

by AnomalousMonk (Chancellor)
on Feb 09, 2018 at 21:07 UTC ( #1208863=note: print w/replies, xml ) Need Help??


in reply to Re: creating qr from existing regex
in thread creating qr from existing regex

$re = "(?:$flags:$core)";

That doesn't work: too many  ':' (colons):

c:\@Work\Perl\monks>perl -wMstrict -le "my $string = '/.*uba$/i'; ;; my $flag = qr{ [msixpodual] }xms; ;; my $convertable = my ($core, $flags) = $string =~ m{ \A \s* / (.*?) / ($flag*) \z }xms; die qq{bad rx: '$string'} unless $convertable; ;; my $re = qq{(?:$flags:$core)}; print $re; print 'A: match' if 'uba' =~ $re; " (?:i:.*uba$)
Something like this works:
c:\@Work\Perl\monks>perl -wMstrict -le "my $string = '/.*u\/ba$/i'; ;; my $flag = qr{ [msixpodual] }xms; ;; my $convertable = my ($pattern, $modifiers) = $string =~ m{ \A \s* / (.*?) / ($flag*) \z }xms; die qq{bad rx: '$string'} unless $convertable; ;; my $rx = qr{(?$modifiers)$pattern}; print $rx; print 'A: match' if 'u/Ba' =~ $rx; ;; my $ry = qr{ \A foo $rx }xms; print $ry ;; print 'B: match' if 'foolubatU/bA' =~ $ry; print 'C: match' if 'FoolubatU/bA' =~ $ry; " (?^:(?i).*u\/ba$) A: match (?^msx: \A foo (?^:(?i).*u\/ba$) ) B: match
Note that:
  • I go directly to  qr// form.
  • The modifiers ($flag pattern) implemented vary by Perl version; see perlop.


Give a man a fish:  <%-{-{-{-<

Replies are listed 'Best First'.
Re^3: creating qr from existing regex
by bart (Canon) on Feb 12, 2018 at 11:47 UTC
    Yes, "(?:$flags:$pattern)" is wrong, it should have been "(?$flags:$pattern)". That is: the flags between the leading "(?" and ":" of the standard non-capturing grouping parens, i.e. "(?:$pattern)".

    You can always try to print out a qr/foo/i, to see what perl does natively.

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